Many clinical studies have shown the effectiveness of hyperthermia (HT) as an adjunctive treatment for malignancies, when used in combination with radiotherapy or chemotherapy (Hahn G. M., Hyperthermia and Cancer, 2nd Ed., New York, Plenum, (1982); Scott, R. S. et al, Int. J. Rad. Oc. Biol. Phys. (10(11) 2219-2123, (1984); Lindholm, C. E. et al, Rec. Res. in Cancer Res. 107: 152-156 (1988)).
Efficacy requires that temperatures within a tumor(s) remain above about 43.degree. C. for 30 to 60 minutes, while safety considerations limit temperatures in normal tissues to below 42.degree. C. In hyperthermia treatment, it is therefore necessary to control the temperature throughout the heated volume to better than about 1.degree. C.
Over the past several years, hyperthermia devices have been improved significantly so that it is now possible to focus energy into a given region of the body (Hahn G. M., Hyperthermia and Cancer, 2nd Ed., New York, Plenum, (1982); Field, S. F. and Franconi, C., Technology of Hyperthermia, Dordrecht, Martinus Nijhoff Publishers (1987)). Despite these advances, however, a lack of adequate temperature control has heretofore limited the usefulness of such devices.
Temperatures can be measured with good accuracy by invasive means. This is attained by means such as thermocouples, thermistors or fiber-optic probes. However, only regions in close proximity to the probes can be monitored with these technologies (Gibbs, F. A. et al, Hyperthermic Oncology, 1st Edition, Vol 2, Philadelphia: Taylor and Francis, pp. 155-167 (1984); Cetas, T. C. Cancer Res. (suppl) 44: 4805-4808 (1984)). Furthermore, probe insertion may be painful and hazardous. Various non-invasive methods have previously been proposed to monitor temperature during hyperthermia. It is, however, difficult to achieve deep measurements with microwave radiometry or infrared thermography while ultra-sound, computerized tomography (CT) and active microwave techniques lack the required accuracy or resolution necessary for controlled treatment.
Magnetic resonance imaging (MRI) is a non-invasive and non-ionizing technique which produces anatomical images in any orientation. Its use as a means to "map" temperature was suggested several years ago (Parker, D. L. et al, Med. Phys 10(3): 321-325 (1983); Dickinson, R. J. et al, J. Comput Assist Tomogr. 10(3): 468-472 (1986); Tanaka, H. et al, Nippon Acta Radiol. 41:897-899 (1981)). Unfortunately, these attempts were unsuccessful because the parameter used, the relaxation time T.sub.1, is difficult to measure accurately by MRI and may have a complex relation with temperature (Lewa, C. J. and Majewska, Z., Bull. Cancer (Paris), 67: 525-530 (1980); Jolesz, F. Z. et al, Radiology 168: 49-253 (1988)).
On the other hand, there is a well known relationship between molecular diffusion and temperature (Simpson, J. H. and Carr, H. Y., Phys. Rev. 111: 1201-1202 (1958)).
It was recently shown that temperature imaging in phantoms can be obtained with good accuracy and resolution (better than 0.5.degree. C./cm) by means of magnetic resonance imaging of molecular diffusion (LeBihan, D. et al, Radiology 171: 853-587 (1989); U.S. patent application Ser. No. 07/324,101 filed on Aug. 19, 1988 by the present inventors, the text of which describes the method of imaging molecular diffusion by NMR is incorporated herein by reference). The same technique was also shown useful to evaluate tissue perfusion (LeBihan, D. et al, Radiology 168: 497-505 (1988)), the dominant physiological mechanism for removing heat during hyperthermia (Hahn, G. M., Physica and Technology of Hyperthermia, Boston: Martinus Nijhoff Publisher, pp. 441-447 (1987); Shitzer, A. and Eberhart, R. C. Ed. Heat Transfer in Medicine and Biology, New York: Plenum (1985); Delannoy, J. et al, Int. J. Hyperthermia (1989), in press). Also, recently it was speculated that MR spectroscopy can be useful to monitor tumor metabolism (Vaupel, P. W. et al, Proc. SMRM, Vol. 1, p. 412 (1988 )).
U.S. Pat. No. 4,230,129 to Le Veen discloses a method of heating body tissue and monitoring temperature changes in the tumor in real time with the aid of a scintillation detector. The method provides for the coupling of RF energy to the patient's body to avoid any significant heat absorption in the fatty tissues. This is obtained by focusing the RF energy on the tumor with an orbital movement of the applicator so that energy is not constantly being applied to the same confined area within the patient's body. U.S. Pat. No. 3,991,770 to Le Veen issued from the parent application U.S. Pat. No. 4,230,129 to Le Veen and has claims directed to a method of treating a tumor in a human by placing the part of the human body containing the tumor in a radiofrequency electromagnetic field to heat the tumor tissue and cause necrosis of the tumor without damaging the adjacent normal tissue.
U.S. Pat. No. 4,186,729 to Harrison discloses an improved electrode for use with an apparatus employing RF energy to produce RF-induced hyperthermia of living animal tissue. The temperature is measured by means of an inserted thermistor.
U.S. Pat. No. 4,346,716 to Carr discloses a microwave system applied to the detection of cancerous tumors. The system combines in a single unit a passive radiometer with an active microwave transmitter in a hand-held unit for heating subsurface tissue. It also provides a radiometer for the remote detection of temperature.
U.S. Pat. No. 4,848,362 to Larsen provides a method for therapeutic deep heating of musculoskeletal tissue with an improved transducer serving simultaneously to couple power from a generator into the patient and to sense the therapeutic response produced. A single unit generates a heating RF signal and detects its thermal response. The response is then used to control the treatment. Both heating and sensing are accomplished by one transducer and one apparatus if dielectric heating is employed. If other forms of heating are used, e.g., ultrasound, the sensor still is present but the apparatus is modified by replacing the high power electromagnetic source with a low power source version.
U.S. Pat. No. 4,815,479 to Carr provides a system and associated method combining microwave detection (radiometry) with microwave heating (hyperthermia) for the treatment of cancer. A plurality of antennas are provided which are disposed over the tumor site in order to separate signal channels. This permits the adjustment of the phase of the separate antenna signals to maximize the signal detected at the microwave radiometric detector.
U.S. Pat. No. 4,632,128 to Paglioni et al. discloses an apparatus for heating which includes an antenna provided with at least one convolution of conductor centered on an axis, the antenna being adapted for heating a surface upon receipt of electrical power. A non-contacting temperature sensor is provided centered on the axis of the antenna with a field of view directed along that axis. A method of analysis and corrective adjustment for relief of nerve interference in the human body is provided which scans subcutaneous microwave emissions of the spinal column, collects and converts the emissions into a visual output, compares with a normal pattern of emissions, determines areas of deviation pinpointing stress, applies a manual corrective adjustment to the spinal column, and monitors throughout the corrective treatment.
None of the methods known in the art and described above provide the simultaneous capability of a hyperthermia applicator and the MRI monitoring of the temperature produced in a human body part during treatment.
Accordingly, there is still a need for an improved apparatus for hyperthermia treatment.